The importance of the gastrointestinal barrier is highlighted by the seriousness of the many diseases in which the gastrointestinal barrier is damaged. Like epithelial cells in other locations, the colonocyte must respond to injury with a genetically programmed repertoire of adaptations. Understanding the function of this gene program in the context of inflammatory bowel disease is obviously of importance. Currently little is known about the mechanisms orchestrating this response, and even less is known about the scale of the response itself. Utilizing techniques for examining gene expression on a genome-wide scale (hybridization to high density DNA arrays), we have identified a number of genes which are markedly induced following epithelial injury. A number of these genes exhibit homology to genes known to participate in an evolutionarily conserved injury response. p38 MAP kinase signaling pathways are leading candidates for mediating the transcriptional programs activated by injury. Few data are available since the reagents necessary to examine the individual p38 isoforms have not been previously available. We have assembled all the necessary reagents and present preliminary data showing intestinal epithelial p38 MAP kinase is strongly activated by injury. This proposal is closely related to our original K08 award (DK0245703). In the K08, we proposed the original hypothesis that MAP kinase pathways were involved in the transduction of epithelial injury-signaling. The K08 specific aims were focused on characterization of MAP kinase pathways activated in response to injury. We have made substantial progress on these aims. As an extension of this work, we have begun to examine the gene program expressed as a consequence of p38 MAP kinase pathway activation. We now propose the hypothesis that p38 MAP kinase isoforms mediate the intestinal epithelial response to injury by direct transcriptional control of an evolutionarily conserved injury response gene program. Using newly available tools, we will focus our efforts on the following two aims: Aim 1. Investigation of the gene program activated by colonic epithelial injury, and Aim 2. Investigation of the role of individual p38 MAP kinase isoforms in the regulation of injury-induced gene expression. From these studies, we anticipate increasing our understanding of the basic molecular mechanisms responsible for mucosal resistance and injury repair. This work will also provide the necessary foundation for future studies examining this gene program in mucosal disease, such as ulcerative colitis. Finally, this proposal will address a large gap in our current understanding of the physiologic role served by individual p38 isoforms.